1. Field of the Invention
The present invention relates to a dual antenna arrangement for a portable transceiver and, more particularly, to a printed circuit antenna which is electrically coupled to or decoupled from a monopole antenna depending upon whether the monopole antenna is in an extended or retracted position.
2. Description of Related Art
It is well known in the portable transceiver art for a second smaller antenna to be utilized in conjunction with an extendable whip antenna. Because a whip antenna can be cumbersome when extended, it is normally preferred that it be retracted except when the transceiver is actively being utilized. The second antenna may be positioned internal of the transceiver housing (e.g., U.S. Pat. No. 4,958,382 to Imanishi and U.S. Pat. No. 5,138,329 to Saarnimo et al.) or as a separate antenna element located around or adjacent the whip antenna (e.g., U.S. Pat. No. 4,121,218 to Irwin et al.).
The internal antennas utilized in U.S. Pat. Nos. 4,958,382 and 5,138,329 are adequate for their intended purpose, but do not work in conjunction with their respective extendable antennas. This not only reduces the effectiveness of these antenna systems, but also may cause a time period where neither antenna is able to radiate.
The helical antenna in U.S. Pat. No. 4,121,218 is disclosed as being positioned around or adjacent to the whip antenna. While the helical antenna is relatively small in size (since it has an electrical length greater than its physical length), it is desired that an even smaller antenna be utilized which has an electrical length at least as great. Further, the distance of separation between the helical antenna and the whip antenna has a direct relationship on the capacitive coupling between them. This distance of separation also is a factor with regard to the impedance matching between the antennas, which may create the need for a compromise as to an optimum separation. Moreover, as noted in a patent application entitled "Printed Sleeve Monopole Antenna" having Ser. No. 08/459,237, which is owned by the assignee of the present invention, one disadvantage of a helical antenna is a reduction in its operating radiation bandwidth due to changes in the input impedance over frequency. In particular, this reduction in bandwidth results from the combination of lower radiation resistance due to smaller antenna size and a larger amount of stored energy causing a high Q.
It has also been found that physically small antennas (relative to the wavelength in free space) have higher energy storage in the reactive near field than electrically equivalent but physically longer antennas. Energy storage in the reactive near field is a mechanism by which energy is coupled to lossy media (e.g., human tissue) located in the reactive near field. Thus, for a given transmitted output power level, physically small antennas increase the energy coupling to the user of a portable transceiver device and emit non-ionizing, electromagnetic RF energy.
Accordingly, it is a primary object of the present invention to provide a dual antenna arrangement for a portable transceiver which permits radiation by a monopole antenna in an extended position and permits radiation by a printed circuit antenna when the monopole antenna is in a retracted position.
It is another object of the present invention to provide a dual antenna arrangement for a portable transceiver in which the size of the printed circuit antenna is minimized.
It is still another object of the present invention to provide a dual antenna arrangement for a portable transceiver where the antennas are matched for optimal transfer of power between them.
Yet another object of the present invention is to provide a dual antenna arrangement for a portable transceiver where the level of power transmitted is dependent upon which antenna is used.
Still another object of the present invention is to provide a dual antenna arrangement for a portable transceiver having a direct electrical connection between the two antennas.
These objects and other features of the present invention will become more readily apparent upon reference to the following description when taken in conjunction with the following drawing.